1. Field of the Invention
The present invention relates to an optical element module comprising at least one optical element and a mounting substrate composed of a semiconductor or dielectric material, in which said optical element is mounted on a top surface thereof.
2. Description of Related Art
Optical element modules in which a semiconductor laser and an optical fiber are mounted on a silicon substrate using a passive alignment technique have been conventionally proposed. The passive alignment technique, in which the optical fiber is embedded in a V-shaped groove formed on the surface of the silicon substrate and the semiconductor laser is mounted at a predetermined position, allows the optical fiber and the semiconductor laser to be fixed at respective predetermined positions without adjusting the optical axes. In an optical element module thus configured, an electrode of the semiconductor laser is electrically connected to an electrode layer formed on the silicon substrate, so that an electrical signal is input to the semiconductor laser via this electrode layer. Such a configuration, however, is disadvantageous in that high frequency characteristics of a signal to be input to the semiconductor laser are lowered due to a high dielectric loss of the silicon substrate.
An optical element module in accordance with one aspect of the present invention aims to improve high frequency characteristics of a signal to be input into an optical element, and comprises an optical element; a mounting substrate composed of a semiconductor or dielectric material and supporting said optical element on a top surface; and a transmission line member at least partially mounted on the top surface of said mounting substrate and electrically connected with said optical element.
The above optical element module, in which electrical connection with the optical element is achieved through the transmission line member, can improve high frequency characteristics even when the mounting substrate is composed of a semiconductor or dielectric material.
In the above optical element module, said mounting substrate may have a groove on the top surface, and at least a part of said transmission line member may be mounted on a bottom surface of said groove. In this optical element module, said groove may be formed as a cut out portion which is removed from a side surface of said mounting substrate. Also, said groove may be formed such that the height of said optical element at a top surface is substantially the same as the height of said transmission line member at a top surface.
The optical element module according to the above aspect may further comprise a connecting member for electrically and physically connecting said optical element and said transmission line member on the side of the top surface of said optical element. Thus, inductance components of the connecting member can be reduced, thereby further improving the high frequency characteristics of the optical element module.
In the above optical element module having a groove on the top surface, said groove may be formed such that the bottom surface thereof and said transmission line member are of substantially the same width. This facilitates positioning of the transmission line member with regard to the bottom surface of the groove. Further, said mounting substrate may comprise a bottom electrode formed at the bottom surface of said groove.
In the above optical element module, said transmission line member comprises a conductor layer formed on substantially the entire back surface of said transmission line member for supplying a ground potential to said optical element via said bottom electrode, and a conductor line formed on the top surface of said transmission line member for transmitting a signal to said optical element. Since a ground potential is thus supplied to the conductor layer and the bottom electrode, a variation in the ground potential is small even when a high frequency signal is input to the optical element. This leads to further improvement of the high frequency characteristics of the optical element module.
In the above-described optical element module having a groove formed on the top surface, said mounting substrate may be provided with a bottom electrode extending through the back surface and a side surface of the substrate to the bottom of said groove. Due to the thus-increased area of the bottom electrode, the high frequency characteristics can be further improved. Further, said mounting substrate may also be provided with a bottom electrode extending through the back surface and a side surface of the substrate having a beveled corner to the bottom of said groove. Because the corner of the side surface of the substrate is beveled, peeling of the bottom electrode off of the groove bottom can be prevented.
The above optical element module may comprise a resin sealing member for sealing said optical element, said mounting substrate, and said transmission line member. This leads to further improvement of the high frequency characteristics.
Further, in the above optical element module, said optical element may be a semiconductor laser or a semiconductor laser comprising a modulator. Also, said mounting substrate may be made of silicon. In addition, the above optical element module may comprise an optical fiber receiving light emitted from said optical element, or an optical fiber which is mounted on a V-shaped groove formed on the top surface of said mounting substrate and receives light emitted from said optical element.
An optical element module in accordance with a second aspect of the present invention comprises an optical element; a mounting substrate composed of a semiconductor or dielectric material and supporting said optical element on a top surface, said mounting substrate having a plurality of grooves formed on said top surface; and a plurality of transmission line members at least partially mounted on a bottom surface of any of said plurality of grooves and electrically connected with said optical element.
With the above-described optical element module, the high frequency characteristics can be improved when a plurality of transmission line members are necessary.